Wireless communication systems, such as the 3rd Generation (3G) of mobile telephone standards and technology, are well known. An example of such 3G standards and technology is the Universal Mobile Telecommunications System (UMTS™), developed by the 3rd Generation Partnership Project (3 GPP™).
The 3rd and 4th generations of wireless communications, and in particular systems such as LTE, have generally been developed to support macro-cell mobile phone communications. Here the ‘phone’ may be a smart phone, or another mobile or portable communication unit that is linked wirelessly to a network through which calls are connected. Henceforth all these devices will be referred to as mobile communication units. ‘Calls’ may be data, video, or voice calls, or a combination of these. An increasing proportion of communications involve data rather than voice, and are technically referred to as being a ‘connection’, rather than a ‘call’.
Macro cells utilize high power base stations to communicate with wireless communication units within a relatively large geographical coverage area. The coverage area may be several square kilometers, or larger if it is not in a built-up area.
Typically, mobile communication units communicate with each other and other telephone systems through a network. In a 3 G system, this is the ‘Core Network’ of the 3 G wireless communication system, and the communication is via a Radio Network Subsystem. A wireless communication system typically comprises a plurality of Radio Network Subsystems. Each Radio Network Subsystem comprises one or more cells, to which mobile communication units may attach, and thereby connect to the network. A base station may serve a cell with multiple antennas, each of which serves one sector of the cell. Often a cellular wireless communication system is described as comprising two parts: the network; and the mobile communication units.
FIG. 1 provides a perspective view of one prior art wireless communication system 100. The system of FIG. 1 comprises a network of base stations, comprising BS1 with reference 110, BS2 with reference 120, BS3 with reference 130, BS4 with reference 140 and BS5 with reference 150. Only one mobile communication unit 105 is shown. In a real network, there may be anywhere from thousands to millions of mobile communication units.
A base station such as base station 110 communicates with mobile communication unit 105. Base station 110 allows mobile communication unit 105 to place calls through the network, and receive calls routed through the network to base station 110.
Base station 140 has been shown as having a coverage area 142. If base station 140 had an omnidirectional antenna, and the terrain were flat, then coverage area 142 might be circular. However, both the shape and extent of the coverage areas of a typical base station depend on many variables, and may change with time.
Controller 160 manages calls within the wireless communication system 100. Controller 160 would be linked to all the base stations BS1-BS5, but the links are not shown in order to keep FIG. 1 simple to interpret. Controller 160 may process and store call information from the base stations shown in FIG. 1, plus many other base stations not shown in FIG. 1. In a UMTS network, controller 160 may be linked to the base stations via one or more Radio Network Subsystems.
There may be significant advantage in knowing where in wireless communication system 100 a mobile communication unit 105 is located. Prior art wireless communication systems have provided a variety of solutions to the problem of ‘geolocating’ mobile communication unit 105. One known solution involves providing specific equipment within the mobile communication unit that can measure location, such as a GPS unit. However, many users switch off the GPS function on their mobile communication units. Partly as a consequence, reported GPS details are highly infrequent. As little as one call in ten-thousand connections might report a GPS coordinate.
One prior art solution indicates that absolute power transmission levels can be used to geo-locate the mobile station. See for example “Mobile Cellular Location Positioning: An Approach Combining Radio Signal Strength Propagation and Trilateration”, M. F. Khan, Masters Thesis, University of Johannesburg, November 2009 which is herein incorporated by reference in its entirety. However, power measurements in event-driven technologies, such as LTE, can be relatively infrequent. Even where a system or mobile communication unit has the capability of performing geolocation based on absolute power measurement, it may remain very important to make use of whatever alternate sources of information are also available.
Co-pending U.S. patent application Ser. No. 13/311,132, with applicant reference OPT004P326, which is herein incorporated by reference in its entirety, indicates that differential power levels can be used to geo-locate a mobile unit. A mobile communication unit provides a measurement of the difference in signal strengths that it receives from at least two base stations. The difference value can be compared to one or more contours of constant power difference, for signals received by subscriber mobile communication units in the system. An estimate of location can be obtained from this comparison. However, differential power techniques can be limited in scenarios where there are few pilot signals to make use of.
Patent application WO2010/083943A, which is also incorporated by reference in its entirety, shows a further technique, which uses signal strength and timing data derived from the mobile communication unit itself, along with network configuration data provided by the network operator, to locate the mobile communication unit.
Co-pending U.S. patent application Ser. No. 13/369,591, with applicant reference OPT004P330, and is hereby incorporated by reference in its entirety indicates that a database of ‘known’ signatures can be used to aid in locating a mobile communication unit operating in a mobile communication system. Each known signature comprises a location measurement or estimate, together with radio frequency and other measurements that were obtained by a mobile communication unit at that location at a particular time. Examples of the ‘other measurements’ that may be obtained by a mobile communication unit are: control information; a set of cells observable by the first mobile communication unit; and received power level information, for signals received from the observable cells.
The use of this database of known signatures enables position estimates to be derived, at least for any mobile communication devices that report similar values of the radio frequency and other measurements to those of a known signature. When a ‘match’ of such similar values is found, the mobile communication device concerned can therefore be assumed to be at the location at which the known signature was recorded.
U.S. patent application Ser. No. 13/369,591 also employs ‘context information’. Context information links successive known signatures in the database. When two or more signatures are received from a mobile communication device whose location is unknown, those signatures can be correlated against two or more signatures in the database that are linked by context information.
The invention of U.S. patent application Ser. No. 13/369,591 only allows the estimation of the position of a mobile communication device if there is a match between a known signature in the database and the values of the radio frequency and other measurements reported by that mobile communication device. This approach therefore relies on the database having many known signatures. For a cellular two-way radio system, the database may require hundreds of thousands or millions of known signatures. Obtaining these known signatures may be difficult. One approach is to collect signatures having location information by employing ‘drive testing’ and/or ‘indoor-walk-testing’. Such testing relies on moving a test mobile communications device through a network, in order to collect accurate position measurements from the mobile communication device and at the same time measure, for those positions, the values of radio frequency and other measurements.
Drive-testing and indoor-walk-testing have the disadvantages that:
(i) Drive- and walk-test signatures may not be easily obtained in the areas most frequented by actual users. This is because some areas are not accessible for either drive- or walk-testing, such as private company premises.
(ii) Signatures can be expensive to obtain over extensive areas.
Signatures obtained from drive- or walk-testing can be augmented by selecting data from the Operation Support System (OSS) of the mobile communication system. The OSS holds measurements made by many or all of the subscriber mobile communication units that operate in a mobile communication system. Some or all of the calls made during drive- or walk-testing will result in a record being created in the OSS. In some systems, the record of the call from the test mobile communications device and the corresponding record from the OSS both contain identification information for the test mobile communications device. If this is the case, then the common identification information can be used. If the correct individual record can be retrieved from the OSS by matching its identification information with the identification information for the test mobile communications device used in the drive or walk testing, then the records can be combined. In particular, the record retrieved from the OSS may contain measurements made by the mobile communication system that can be added to the record of the same call that was made by the test mobile communications device itself as part of drive or walk testing.
Thus the identification information in both records allows the two records to be identified as being from the same mobile communication device. This may in turn then allow the two records to be synthesized into a more comprehensive signature than was obtained directly from the test mobile communications device.
Cellular wireless communication systems have faced the disadvantages that signatures may be expensive to obtain by known methods, and may not be representative of the areas where users make calls. Hence, there is a need for an improved method for generating reference signatures in a mobile communication system, such as an LTE, GSM or UMTS network.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve under-standing of embodiments of the present invention.